Electron discharge device



March 19, 1940. E

c. s. BULL :1- AL ELECTRON DISCHARGE DEVICE Filed Oct. 30, 1936 OUTPUTOSC/LIAwB l/VPl/T' Mam/Mme wPl/r.

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Patented Mar. 19, 194i) are rice f f ELECTRGN DISCHARGE DEVICE CabotSeaton Bull, Uxbridge, and .iohn Edgar Keyston, Hiliingdcn, England,assignors t0 Electrio d; Musical Industries Limited, Hayes, I Middlesex,England, a British company Application October so, 1936, Serial In GreatBritain November 2,

8 Claims.

The present invention relates to electron discharge devices.

The invention is particularly concerned with discharge devices of thekind which comprise means for producing a beam of electrons, one or morecollecting electrodes, and. means for defleeting the electron beam inaccordance with an. applied controlling signal in such a manner that theelectron current passings to the collecting electrode or electrodesvaries in dependence upon the controlling signal.

Most known devices of the kind referred to above have the disadvantagein practice that the ratio of extent of variation of collectingelectrode current to the amplitude of the controllin signal-that is, thedeflection sensitivity of the device-is undesirably low. In an attemptto overcome this clifficulty, it has been proposed to provide means,such for example as a reflector,

for causing electrons on their Way to the collecting electrode to followpaths which are longer than the distance between the electron source andthe collecting electrode measured directly, whereby the extent of thedeflection of electrons over the collecting electrode in a lineardirection which corresponds to a certain angular deflection produced bythe deflecting means is in creased; the arrangement is, however, suchthat the angular defiectionoi the electron beam mains substantiallyconstant at all points in the electron path, or at least is not greatlyincreased, the angular deflection being the angle made with thedirection of the beam in the undeflected condition, by the beam, when adeflecting signal of unit strength is applied to the deflecting means.

It is an object of the present invention to provide new or improveddischarge devices of the kind referred to which have a greaterdeflecting sensitivity. than known arrangements of that kind.

The present invention accordingly provides an electron discharge devicehaving means comprising a source of electrons ior emitting an electronbeam, a collecting electrode or system of collecting electrodes forreceiving said beam, and first deflecting means for deflecting said beamin response to applied electric deflecting signals, wherein there areprovided second defleeting means for increasing the angular deflecticnofthe beam produced by the first defleeting means, the arrangement beingsuch that, over a part only of the range of deflection of the beam bythe first deflecting means, the second deflecting means give to the beama coml lo. 108,466 1935 ponent of motion in a direction opposite to thatof the electrons leaving the first deflecting means.

It may be arranged that if a given deflecting signal causes theelectronbeam to be deflected by the first deflecting means through an angle A,the effective angular deflection of the beam ai'te-r deflection by thesecond deflecting, means is given approximately by (BA) over a range or"values of A; the angle 3 can be made greater than 96, and can bearranged to approacho closely to 188; the angle A can convenientlybearranged to have a maximum value of the order of 4:5", and it will thusbe clear that the second deflecting means can be arranged to produce aneffective increase in the angular deflection produced by the firstdeflecting means of at least twice; in general, an increase of much morethan twice can be obtained.

The second deflecting means may be so constituted and arranged that, inoperation, they; produce a deflecting field the equipotential surfacesof which are substantially of saddle-back shape. As will appearhereinafter, however, the second deflecting means may be arranged toproduce fields of other forms, for example, holds the equipotentialsurfaces of which conform to the surfaces of co-axial cylinders.

Other features of the invention will appear from the followingdescription and appended claims. I

Various embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawing, in which,

Fig. l. is an explanatory diagram to which reference will be made forthe purpose of eluci datingthe principles of the invention.

Fig. 2 illustrates a modification of a detail of the arrangement of Fig.1.

Fig. 3 is a diagrammatic drawing of a dis charge device according to theinvention, and a circuit therefor.

Fig. 4 is an explanatory diagram.

Fi 5 illustrates further construction or" the device according to theinvention and a circuit therefor, and t Fig. 6 is a cross-sectional Viewof the electron discharge device of Fig. 5, the cross-section being amedian one along the broken line in Fi 5.

Referring to Fig. 1, four electrodes P, P,-N, N are arranged as shown toform four sides of a 50 rectangular box, each electrode being insulatedfrom the two adjacent electrodes. The electrode N is provided with anaperture at itscentr'e, and outside the box and facing this aperturethere is located an electron-emitting cathode C.,- Q

Means (not shown) which may take any suitable form are provided fordirecting a beam of electrons from the cathode C towards the aperture inelectrode N. Between the cathode and the aperture there are providedfirst deflecting means for deflecting the beam in a plane perpendicularto the planes of the four electrodes which form the box, thesedeflecting means cenveniently taking the form of a pair of plates D andD adapted to provide electrostatic deflection; the first deflectingmeans may alternatively comprise coils adapted for electromagneticdeflection. The deflecting means D, D are coupled in operation, to asource (not shown) of deflecting signals; the apertured electrode N andthe electrode N opposite thereto are both maintained at or near tocathode potential and the electrodes P and P are maintained at suitablepositive potentials with respect to the oathode.

It will be assumed that the incident direction of the electron beam isnormal to the electrode N when the deflecting means D, D areinoperative. When the deflecting means produce only slight deflection ofthe beam to the left (it being assumed that the observer is looking intothe box through the aperture in electrode N) the beam follows an almoststraight path to a point close to the opposite low potential electrode.It then suffers a rapid deflection to the left in a substantiallyparabolic curve (this deflection may be about 150 for example) afterwhich it follows another almost straight path and terminates on thatedge of the high potential electrode P which is nearer the aperturedelectrode N. The path followed by the beam in these circumstances isindicated by the dotted line A. When the cleflecting means D, D producegreater angular deflection, the beam tends to travel up the potentialsaddle formed between the electrodes P, P, N, N by the potentialsthereon, and when the deflection due to plates D, D exceeds a criticalvalue, the beam is deflected through less than a right-angle and followsa path such as that indicated by the full line B.

The electrodes P, P, N, N constitute the second deflecting means, thedeflecting field which they produce being one of saddle back form. Thearrangement is such that the deflection produced by the seconddeflecting means varies inversely in dependence upon that produced bythe plates D, D; electrons which are deflected by the plates through anangle which is less than a critical value are given, by the influence ofthe saddle back field, a component of motion in a direction oppositefrom that in which they leave the oathode, and electrons which aredeflected by the plates D, through an angle greater than the criticalvalue continue in motion in a direction having a component in thedirection of emission. Thus a small change in the deflection due to thedeflecting plates D, D produces a considerable change in the deflectionwhich the beam suffers within the box P, P, N, N. When the platesdeflect the ray to the right, the effect with respect to thehigh-potential electrode P is the same as for the high-potentialelectrode P in the case described above.

The device described with reference to Fig. 1 may be modified for use inamplifying electrical oscillations; for this purpose a part of one orboth of the high-potential electrodes P, P may be insulated from theremainder thereof and connected to its associated source of potentialthrough a load impedance.

Fig. 2 illustrates a part of the device of Fig. 1 modified in the mannersuggested; the electrode P of Fig. 1 is replaced in Fig. 2 by two planeelectrodes S and T, electrode S being biassed to a positive potential bybattery B, and electrode T being connected through a load resistance Rto battery B. By virtue of the shape of electrode T a portion of thebeam of varying magnitude falls in operation, on this electrode. Thepotential across or the current in the load impedance R may be used tocontrol a further stage of arnplification or may be used directly formany other purposes.

If it is desired to operate the device of Fig. l as a simple relay, theoutput may be taken from the whole of one of the high potentialelectrodes P, P or from both these electrodes in pushpull.

A further arrangement according to the invention is illustrated in Fig.3; referring to Fig. 3, a cathode C and first deflecting means in theform of a pair of electrostatic deflecting plates D, D are enclosedwithin a cylindrical electrode The axis of the electrode E is coincidentwith the undeflected direction of the electron beam and the cylinder ismaintained, in operation, at or near cathode potential. In front of thecylinder E and intersecting the axis thereof at right-angles, is locateda rod-shaped electrode F which is arranged perpendicular to the plane inwhich the electron beam is deflected and is also maintained, inoperation, at or near cathode potential.

Five part cylindrical electrodes P1, P2, P2, P4. P5, are arranged in acylindrical surface the axis of which is parallel to the rod F and issituated substantially mid-way between the rod F and the end of theelectrode E adjacent the rod. At least a part of the cylindricalelectrode E is located within the cylindrical surface in whichelectrodes P1, P2, P3, P4, P5 lie. The part-cylindrical electrodes P1,P2, P3, P4, P5 are bounded in part by lines parallel to the axis of thecylinder of which each forms a part. Measuring angles from the centre ofthe cylindrical surface, taking the direction from which the beamnormally enters as axis and measuring in a clockwise direction, theedges of the part-cylindrical electrodes occupy approximately thefollowing positions: P1, 30 and P2, and P3, and 210, P4, 225 and 255;P5, 270 and 330. The part-cylindrical electrodes are all maintained atsuitable positive potentials with respect to the cathode. As in thearrangement of Fig. l, the electrons, after deflection by the firstdeflecting means, enter a saddle-shaped potential field and aredeflected in a manner similar to that described with reference to Fig.l, the electrodes by which the saddle-shaped potential field aregenerated serving as second deflecting means. When the deflecting platesD, D are inoperative, the beam is reflected by the field in theneighbourhood of the rod F and terminates on P1; with maximum deflectionby the deflecting plates D, D, the beam terminates on P3, andinterniediately the beam falls on P2. Thus the curve showing therelation between the current flowing to P2 and the deflection producedby the deflecting plates D, D has the form shown at X in Fig. 4; thecurve starts at zero current for small angular deflection, rises to amaximum current for a certain intermediate deflection and falls to zeroat a greater deflection. By suitably shaping electrode P2 (for exampleby making this electrode of triangular outline instead of rectangular)or by adjusting the current density in various parts of the beam, thecharacteristic curve X can be madesubstantially para-bolic over aconsiderable range, and the device is then suitable for use in avariable gain ampli- The gain controlling bias may be applied to thefirst deflecting means D, D alone or to the low potential rod F or toboth the first defiectingmeans-and the rod. Further, the deflectingsignals may also be applied to the rod. Instead of using P2 as outputelectrode, P1 and Ps may be connected together to serve this pur-' Therelationship between angular defiec a maximum) in theneighborhood of aboundary (which may be defined by one .or more electrodes) and does nottherefore continue beyond this minimum (or maximum).

In the arrangement according to the invention which is illustrated inFigs. 5 and 6, the cathode C is in the form of an elongated shallowrectangular box containing a suitable heater (not shown) and coated onits major surface a with electron- For the sake of description theelectron emitting surface will be considered.

emitting material.

as being so disposed that its longer edges extend downwardly into thepaper, and the median horizontal line passing normally through thecentre cathode lie near the plane. containing the electron emittingsurface. Extending between the plates M, M2 in a plane at right anglesto the axis of the arrangement-is located a diaphragm MD of length equalto that of the plates M, M2, the diaphragm having a slot therein asshown. The slot is located symmetrically about the axis and extendsalmost thevwhole length of the diaphragm MD. The width of the slot isconsiderablyless than the distance between the plates M, M2 constitutingthe modulating electrode.

On the side of the modulating electrode remote from the cathode a firstanode is located; the first anode comprises two plates G, G2 arrangedcoplaner respectively with and spaced a small distance from the twoplates M, M2 of the modulating electrode. Extending centrally betweenthe first anode plates is a diaphragm GD similar to that of themodulating electrode, except that the slot GD of the first anode issomewhat wider than the slot MD of the modulating electrode.

' The width of the plates G, G2 of the first anode In some cases,instead of respectively with and spaced a small distance from the platesof the first anode. The width of the plates ofthe second anode may beabout twice the width of the plates of the first anode. A diaphragm HDsimilar to that in the modulating electrode extends between the endsremote from the cathode of the plates H, H2 of the second anode. Twoelectrostatic deflecting plates D, D2 are located within-the secondanode, the plates lying in planes parallel to and equidistant from 10the axis of the arrangement and being more remote from the cathode thanthe centre of the second anode.

Beyond the second anode a rod-shaped electrode F is arranged to lie in aplane extending vertically downwards into the paper through the axis ofthe arrangement. The distance between the end of the second anode I-I,H2 and the rodshaped electrode F may be somewhat less than the length ofthe second anode.

Five part cylindrical electrodes P1, P P3, P4 and P5 are arranged in acylindrical surface about the rod-shaped electrode F as axis, the radiusof the cylinder being slightly less than the distance of the rod-shapedelectrode from the end nearer thereto of the second anode H, H2. Thepart cylindrical electrodes are bounded in part by lines passingvertically downwards into the paper, the angles which the planes throughthese lines and the rod-shaped electrode make with the axis of thearrangementzero direction being that of a line from the rod-shapedelectrode towards the cathode-being as follows: P1,

10 and 55"; P2, 70 and P3 and 210; P4, 225 and'290; P5, 305 and 350.

It will be seen that the adjacent edges of P1 and P5 form a slot closeto and parallel with the slotin the diaphragm HD in the second anode.

In operation, the modulating electrode M, M2 is used to controlthe'intensity of the electron beam leaving the cathode and is maintainedat a negative biasing potential with respect to the cathode. I The firstand secondanodes G, G2 and H, H2 are maintained at suitable positivepotentials with respect to the cathode and serve as anelectron lens tocause a narrow elongated or ribbon like beam of electrons to'pass outthrough the diaphragm HD in the second anode. This beam of electrons maybe deflected by applying a deflecting potential difference between thede-" fiecting plates'D', D2;

The rod shaped electrode Fis maintained at or near cathode potential andthe electrodes P1.

P2, P3, P4, P5 are maintained at suitable positive I potentials withrespect to the cathode.

The arrangement described with reference to Figs. 5 and 6 operates in amanner similar to that of the arrangement of Fig. 3; the arrangement ofFigs. 5 and 6 has, however, several imequipotential surfaces conform tocoaxial cylin- I ders the common axis of' which isco-incident with therod-shaped electrode F. The angle between the direction of electronsentering the field within electrodes P1 to P and the direction of thelines of force of this field (which may be considered as the directionin which an electron tends?! to move due to the field at the pointconsidered may be almost as great as 180.

In the arrangement of Figs. 5 and 6 there are three methods ofcontrolling the magnitude of the electron stream impinging on any one ofthe electrodes P1, P2, P3, P4 and P5. In the first of these, controllingsignals are applied to the modulating electrode M, M2 (which, instead ofbeing formed with an apertured diaphragm may contain a grid constructedof wire mesh or the like). In the second, deflecting signals are appliedto the deflecting plates D, D2. In the third, controlling signals areapplied to the rod-shaped electrode F.

Inter-modulation between two signals may be obtained by controlling theelectron stream by the two signals, for example, by applying one signalto the deflecting plates D, D2 and the other signal to the rod electrodeF. The term intermodulation is intended to cover arrangements in which asignal is caused to beat with a second signal of different frequency(such as modulating and superheterodyne arrangements), arrangements inwhich a modulated carrier is caused to beat with an oscillation of thesame frequency as the carrier (homodyne reception) and arrangements inwhich the signal is caused to beat with itself, thereby producing squarelaw rectification.

It is also possible to mix two signals by applying them simultaneouslyeither to the deflecting plates or to the rod-shaped electrode; in thiscase, when the arrangement is such that working on a paraboliccharacteristic takes place, modulated signals free from undesiredsignals are given.

The sensitivity of the arrangement can be further increased by socoupling the deflecting plates D, D2 and the rod electrode F that. asthe plates produce less deflection, the rod electrode becomes morenegative relative to the cathode. This yields a greater degree ofcontrol than that obtained by applying the controlling signal to thedeflecting plates only.

In a further modification the electrode system P1 to P5 is replaced by afluorescent screen held at a suitable positive potential with respect tothe cathode so that the point of incidence of the deflected beam isrendered visible, the fluorescent screen acting as a collectingelectrode. Such an arrangement can be used as a sensitive electrostaticvoltmeter or as a tuning indicator for a wireless receiver, deflectioncontrol being effected either by direct or alternating potentials.

It will be appreciated that, in many cases, the current proceeding tothe collecting electrode system P1 to P5 does not remain in a focusedbeam after being deflected by the rod electrode F. In some cases thedeflection produced by this electrode may be so sensitive that electronsof the incident beam which have different original emission velocitiesare deflected through appreciably different angles. In this case theelectrons which proceed to the collecting electrode system may be spreadout into a spectrum according to their initial velocities. In this casea beam of electrons having a substantially homogeneous velocity may beseparated. from the main beam by providing a suitably shaped narrow slitin the collector system.

The arrangement of Figs. 5 and 6 may be adapted for the generation ofoscillations in the following manner; collecting electrodes P4 and P5are connected to a common load impedance, and are coupled to one ofdeflector plates D and D2. Electrodes P1 and P2 also have a common loadimpedance, and are coupled to the other deflecting plate. Thearrangement is made such that when current passes to electrodes P4 andP5, the beam is deflected by plates D, D2 so that it falls on electrodesP1 and P2, whereupon it is deflected to the right to fall on plates P4and P5 and so on. An output circuit is coupled to the electrodes P1, P2,P4 and Pa in such a manner that an oscillation is set up in the outputcircuit. The frequency of the oscillation can be adjusted by variationof the time constants of the external circuits.

Screening grids, which are maintained in operation at positivepotentials relative to the cathode, may be provided if desired toprevent variations in the potentials of the collecting electrodes fromcausing a distortion of the field within the collecting electrodes, andfrom influencing adversely the operation of the device. When screeninggrids are employed, means may also be provided for preventing thepassage of secondary electrons from the collecting electrodes to thescreening grids; these means conveniently take the form of one or moresuppressor grids maintained in operation, at or near cathode potential.

It is to be understood that the second deflecting means may take otherforms than those described; thus, instead of the single electrode N ofFig. 1 or F of Fig. 3, second deflecting means comprising any desiredarrangement of more than one electrode which produces a suitabledeflecting field may be employed.

The invention is not limited to the arrangements described by Way ofexample above, and many modifications within the scope of the appendedclaims will occur to those versed in the art.

We claim:

1. An electron discharge device having an envelope containing aplurality of electrodes enclosing a space and including anodes forreceiving electrons, two of the said plurality of electrodes beingspaced to provide an aperture, means for projecting a beam of electronsinto the space enclosed by said electrodes through said aperture, acontrol electrode in the path of the beam of electrons for deflectingsaid electrons and another-pair of oppositely disposed electrodesadjacent the beam supply means and on opposite sides of said beam andcooperating with said first control electrode for causing the beam ofelectrons to be shifted from one anode to another during operation ofthe electron discharge device,

2. An electron discharge device having an envelope containing aplurality of electrodes enclosing a space and including a pair ofoppositely disposed anodes for receiving electrons, two of saidelectrodes being spaced to provide an aperture, means including acathode for projecting a beam of electrons into the space enclosed bysaid electrodes through said aperture, a deflecting electrode in thepath of said beam of electrons and maintained at cathode potential, 9.pair of oppositely disposed deflecting electrodes adjacent said cathodebetween which said beam passes, said first deflecting electrode and saidpair of deflecting electrodes cooperating during operation of the tubefor deflecting the electron beam between said oppositely disposedanodes.

3. An electron discharge device having an envelope containing aplurality of arcuate shaped electrodes enclosing a space, two of saidelec trodes being spaced to provide an aperture, a deflecting electrodewithin said space, means including a cathode for projecting a beam ofelectrons through said aperture into said space towards said deflectingelectrode and a pair of oppositely disposed deflecting electrodesbetween which the beam passes positioned adjacent the cathode, said pairof deflecting electrodes and said first deflecting electrode cooperatingduring operation of the tube for deflecting the beam of electronsbetween the electrodes enclosing said space.

4. An electron discharge device having an envelope containing aplurality of arcuate shaped electron receiving electrodes coextensivewith each other and positioned around a common axis to enclose a space,a deflecting electrode positioned within the space enclosed by saidarcuate shaped electrodes and at the axis of said space and parallel tosaid arcuate shaped electrodes, a beam forming device including acathode for pro jecting an electron beam into the space enclosed by saidarcuate shaped electrodes, a connection between the first deflectingelectrode and said cathode, and a pair of deflecting electrodes betweensaid cathode and said first deflecting elec-' trode between which thebeam of electrons passes.

5. An electron discharge device having an envelope containing aplurality of rectangular shaped electrodes of arcuate cross-sectionenclosing a substantially cylindrical space, said electrodes beingcoextensive and parallel to each other, a control electrode parallel tosaid arcuate shaped electrodes positioned at the axis of the spaceenclosed by said arcuate shaped electrodes, means for projecting aribbon like beam of electrons into said space towards said deflectingelectrode and including a cathode, a pair of oppositely disposed beamdeflecting electrodes adjacent the cathode through which the beam isdirected, and a pair of focusing electrodes coextensive with the cathodeand with said arcuate shaped electrodes for focusing the beam ofelectrons between said pair of deflecting electrodes.

6. An electron discharge device having an envelope containing aplurality of electrodes enclosing a space and including a pair ofoppositely disposed anodes for receiving electrons, means electrodebeing connected to said cathode, and a source of voltage connectedbetween the output circuit and said cathode.

'7. An electron discharge devicehaving an envelope containing aplurality of arcuate shaped electrodes surrounding a substantiallycylindrical space and including a pair of oppositely disposed anodes, adeflecting electrode within said space positioned at the axis of saidarcuate shaped electrodes, means including a cathode for projecting abeam of electrons into said space towards said deflecting electrode anda pair of oppositely disposed deflecting electrodes between which thebeam passes positioned adjacent the cathode, said pair of deflectingelectrodes and said first deflecting electrode cooperating duringoperation of the tube for deflecting the beam of electrons between theelectrodes enclosing said space, an input circuit connected between saidpair of deflecting electrodes and said cathode and an output circuitconnected between said pair of oppositely disposed anodes and a sourceof voltage connected between the cathode and said output circuit, theother arcuate shaped electrodes not connected to said output circuitbeing connected to an intermediate point on said source of voltagesupply, and a connection between said first deflecting electrode andsaid cathode.

8. An electron discharge device having an envelope containing aplurality of rectangular shaped electrodes of arcuate cross sectionenclosing a substantially cylindrical space, said electrodes beingcoextensive and parallel to each other, a control electrode parallel tosaid arouate shaped electrodes positioned at the axis of the spacesurrounded by said arcuate shaped electrodes, means for projecting aribbon shaped beam of electrons into said space towards said deflectingelectrode and including a cathode, a pair of oppositely disposed beamdeflecting electrodes adjacent the cathode through which the beam isdirected, and a pair of beam focusing electrodes coextensive with thecathode and with said arcuate shaped electrodes for focusing the beam ofelectrons between the first pair of deflecting electrodes, an inputcircuit connected between the cathode and one of said beam focusingelectrodes, an oscillator circuit connected be tween said pair ofdeflecting electrodes and a connection between the cathode and saidoscillator circuit,- anoutput circuit connected between a pair ofoppositely disposed arcuate shaped electrodes, a source of voltagesupply connected between the cathode and said output circuit, theremainder of said arcuate shaped electrodes being connected to anintermediate point on said I source of voltage supply, and a connectionbetween the first deflecting electrode and said cathode,

CABOT SEATON BULL.

JOIN EDGAR KEYSTON.

